su-nav {
    width: 100%;
    height: 100vh;
}

header {
    display: flex;
    position: fixed;
    width: 100%;
    height: var(--x4);
    background: var(--Black);
    color: var(--Black_i);
    justify-content: center;
    align-items: center;
}

main {
    display: flex;
    flex-direction: column;
    height: 100%;
}

#nav-container {
    position: fixed;
    height: 100vh;
    width: 100%;
    pointer-events: none;
}

#nav-container:focus-within::before {
    content: '';
    background: var(--Shadow);
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
}

.button {
    display: block;
    box-sizing: content-box;
    height: 6px;
    border-bottom: 2px solid var(--Gray);
    width: var(--x2);
    margin: calc(var(--x2) - 8px) auto auto var(--x2);
    cursor: pointer;
    pointer-events: auto;
    touch-action: manipulation;
    transition: .3s;
}

.button::before,
.button::after {
    content: '';
    display: block;
    height: 2px;
    border-top: 2px solid var(--Gray);
    padding-bottom: 2px;
}

.button::after {
    border-bottom: 2px solid var(--Gray);
    border-top: 2px solid transparent;
}

#nav-container:focus-within .button {
    pointer-events: none;
    border-bottom-color: transparent;
}

#nav-container:focus-within .button::before {
    width: calc(1.1 * var(--x2));
    transform: translate3d(-2px, 6px, 0) rotate(45deg);
}

#nav-container:focus-within .button::after {
    width: calc(1.1 * var(--x2));
    transform: translate3d(-2px, -5px, 0) rotate(-45deg);
}

#nav-content {
    margin-top: var(--x4);
    width: 300px;
    position: absolute;
    top: 0;
    left: 0;
    height: calc(100% - var(--x4));
    pointer-events: auto;
    transform: translateX(-100%);
    transition: transform .3s;
    will-change: transform;
    contain: paint;
}

#nav-content ul {
    height: 100%;
    display: flex;
    flex-direction: column;
}

#nav-container:focus-within #nav-content {
    transform: none;
}